Simple Object Access Protocol (SOAP) is a protocol for sending messages between computer systems on a network. Messages are placed in an Extensible Markup Language (XML) format and transmitted via the Hypertext Transfer Protocol (http). Since XML and http are commonly available on many computing systems, SOAP offers a convenient means for communication, even among computers operating under different platforms.
A typical SOAP message might consist of a SOAP envelope that is made up of a SOAP header and a SOAP body. The body typically contains the message itself while the header might contain metadata about the message, such as security information. When secure communication is desired between a client and a server on a network, the necessary identifying information, such as a digital certificate, can be included in the SOAP message header.
Some enterprises wishing to communicate securely over a network may be unable or unwilling to use the SOAP messaging format. In that case, another protocol for secure communication is desirable.